Base Class: Rogue
You are a master of poison and how if affects the body. With time you can grow into something great, but for now you have to settle for your current mediocre skill.
Additional Proficiencies
Starting at 3rd level, If you didn't have it already, you gain proficiency with a poisoners kit and the Medicine skill.
Blood's Bane
Starting at 3rd level, you gain the ability to distill your own poisons from your own blood. You may spend an hour and a single hit die, to craft 10 doses of non-magical poison.
Each dose of the poison may be applied to a blade, be injected, or taken orally and have the same affect. If applied to a blade, the poison lasts for 8 hours before losing potency and expiring. The poison deals half your current sneak attack bonus (rounded down) and the target must succeed on a DC(8+prof) Constitution saving throw, or gain the poisoned condition.
Steady Hand
Starting at 9th level, your poison becomes magical. It now counts as magical damage and ignores all non-magical resistances and immunities to poison. Your use of poison also imbues you with a high resistance to its effects, you gain resistance to all poison damage.
In addition, if carefully injected or taken orally, the poisons deal increases to be equal to your sneak attack bonus and deals max damage.
Poisoned Self
Starting at 13th level, your blood becomes poison itself. Whenever you take damage you may spend your reaction to cause your poisoned blood to spread out in a 5ft radius around your body. Each creature in the 5ft radius must make a DC (8+DEX+Prof) Constitution Saving Throw. A target takes X poison damage and is poisoned on a failed save, or half as much damage on a successful one. You may use this ability once per long rest at 13th level and twice per long rest at 17th level.
In addition, your poison now ignores resistance to all poison damage and treat poison immunity as poison resistance.
Kiss of Death
Starting at 17th level, your touch can channel the energy of death into a creature. As an action, you attempt to grapple one creature within 5 feet of you or touch a defenseless creature, and you channel your energy to close them off from life. If the target is grappled or can't defend itself it instantly drops to 0 HP and dies. This ability doesn't work against creatures that are immune to poison damage.
You may use this ability once per long rest.